Annotations and Highlighting

[drbenomycin]

Hi,

Thank you very much for your efforts in maintaining and improving this software, it is very much appreciated. I would love to migrate my slide preparation to Beamer (from Powerpoint) and pympress provides much of the functionality I need for presenting (indeed, it offers more features and this is very attractive), however, there are two items listed under Issues that are preventing me making that move, and I wonder if you are able to update any progress on them, and if they are likely to be addressed soon or are low priority.

Firstly is the issue of exporting a PDF with the 'highlighting'. I understand there are a lot of complexities in doing this, but it is a feature I need. I'm not worried about breaking compatibility with Beamer in my use case. Is there any way to do this currently? I notice that the feature to "remember" highlights when navigating away from and back to slides is present, so I assume this is being retained somewhere.

Connected to this, I see in the Readme this line "Editable PDF annotations: Annotations can be added, removed, or changed, and the modified PDF files can be saved". I can't find any information on what this refers to? I can't figure out how to add annotations. I assume this is different to highlighting because saving the pdf doesn't save my highlights.

Secondly is the issue of having the highlighting tools permanently enabled, rather than reactivating on each slide change. Realistically, this is not actually a show stopper, but would be a nice quality of life feature.

Thanks in advance!

[Cimbali]

Currently editable annotations are only text-based. You can open that window with a by default. Highlights could be saved as pdf annotations too but that needs quite some work I believe. Maybe we could use Poppler.AnnotType.POLY_LINE for everything we generate, but looking at it quickly I’m not sure all of that is exposed through the python bindings.

pympress does correctly render annotations saved to a file from any other pdf viewer though, so if it’s just about displaying some manually added annotations that should work.

[drbenomycin]

For what it's worth, this would essentially replicate the Powerpoint model (not that I advocate that it's a good model). Annotations on slides are editable on a per stroke basis while the presentation is open, but after saving and reopening they are merged into a layer that can be deleted, but not edited.

My understanding is that in pympress the annotations are being stored somewhere, in some format, while the presentation is live (enabling the "Highlight mode > Clear and restore per page number" option) and if you can point me towards any way to access that data such that it can be converted to an image and added to the pdf, that would be wonderful. I'm not a real coder, so I can't help with implementation in pympress itself, but depending on what that data looks like I can probably hack together some solution that fits my specific need (if it is able to be accessed). I don't really want to take more of your time for this, so if there's no easy way to access that, I'll leave it there.

[Edit]:
I just had a look at the code, and I guess a semi-janky implementation could export an image on page change, so in scribble.py > page_change():

        # Remember whatever the current mode, to facilitate switching modes
        self.current_page = (page_number, page_label)

        if self.highlight_mode == 'global':
            return
        elif self.highlight_mode == 'single-page':
            return self.clear_scribble()
        else:
            # Now optionally save the current scribbles
            if current_page is not None and self.scribble_list:
                self.remembered_scribbles[current_page] = self.scribble_list.copy()
                <render scribbles to image (pagenum_scribbles.img)> #pseudocode added 

Unfortunately I'm stuck using the binary version on windows for now, otherwise I might try my hand at this.

[Edit 2]:
Forgive me, sometimes once my brain starts thinking about a problem I find it hard to let go. Looking further at the code and doing some googling, is this as "simple" as using surface.write_to_png ("img.png"); to render a png the same size as the slide? https://valadoc.org/cairo/Cairo.Context.save.html

Oh - by the way, I just found the "Highlight mode > Exit highlight on page change" checkbox that I had previously missed - so apologies for the other part of my query that was already implemented.

[Cimbali]

Would an export of highlights to png files fit your needs? I’m a little confused about your use case/workflow to be honest.

I think the only way to save highlights in the pdf currently, looking at exposed Poppler images, is to render to a cairo surface and then save tot he PDF as a stamp annotation with that surface set as custom image. We could even do a stamp per line if that’s not too heavy, but re-importing would be a bit awkward. The upside is that drawn lines should look the same on all viewers then as we save the rendered image and not the rendering instructions. The downside is, as with all PDF annotations, as soon as you re-build your beamer presentation you lose it all because it’s a new PDF file.

[drbenomycin]

My use case is essentially I present the slides in a teaching context and fill in gaps in the content by annotating them with a stylus. It is useful to be able to retain these after the presentation to share with students. Losing annotations on rebuild of the presentation doesn't matter because I would only be doing that if it was for a new class.

My ideal would be to have them written to the pdf so I can just save at the end of the presentation, but I'm conscious that might not be trivial.

A less good solution that I figured would be easier to implement would be to export a PNG of the annotations (on a transparent background) that I can use other software to add to the pdf. I'm conscious of not asking too much from an open source project when my use case might be very niche.

[Cimbali]

Alright, that makes sense to me now. I suppose a number of people are in your situation too.

[drbenomycin]

Thanks - yes my interpretation of some of the Issues and other Discussions around this is that it's a similar use case where the annotations don't need to be retained when the Beamer presentation is regenerated, but are useful to have.

Thinking further on the merits of a PDF stamp vs. exporting PNG files on a per slide basis. I assume anyone sufficiently technical to be using Beamer would find it trivial to include a PNG file in their Beamer if they did want to retain annotations as part of their presentation after regeneration. Perhaps ultimately the option to do either would be a useful feature. For now, I'm grateful for anything that can be implemented and happy to provide testing and bug reports.